This paper examined the production of unstressed vowels by Brazilian Portuguese (BP) learners of English. More specifically, the aim was to examine the acoustic characteristics of the interlanguage unstressed vowels and to determine whether the language learners' stress assignment in cognate words was targetlike or not. The participants were 20 L1 BP learners of English and two native English speakers who provided the baseline data. Participants read lists of sentences including polysyllabic cognate words with the neutral suffixes "-able" and "-al" (e.g. 'respectable', 'radical'). Participants' productions were acoustically and auditorily analysed and the F1, F2 and duration values measured. The results showed that the L1 BP participants produced a reduced vowel /ə/ with similar acoustic characteristics to the L1 English speakers, differentiating it from /ʌ/ in terms of vowel quality and duration. Despite being able to distinguish between the unstressed and the stressed central vowels, the correct assignment of stress in polysyllabic cognates was challenging for the L1 BP informants. A possible explanation for the non-target-like stress assignment is negative transfer from the L1, in which one of the target suffixes, "-al" (e.g. 'tropical'), attracts stress, contrary to the L2.